Disposal of spent aluminum chloride alkylation catalyst sludge

ABSTRACT

A METHOD FOR SEPARATING ALUMINUM CHLORIDE ALKYLATION CATALYST SLUDGE FROM A MIXTURE OF PRODUCT ALKYLATE AND SLUDGE, IS PROVIDED WHEREIN THE ALKYLATE IS SEPARATED FROM THE SLUDGE AND PASSED THROUGH A WASHING ZONE. THE LIQUID EMPLOYED IN THE WASHING ZONE IS THEN INTRODUCED INTO A HYDROLYSIS ZONE WHEREIN THE SEPARATED SLUDGE IS HYDROLYZED. THE HYDROLYZED SLUDGE IS THEN ALLOWED TO SETTLE AND FORM A WATER PHASE AND AN ORGANIC PHASE. A PORTION OF THE WATER PHASE, WHICH CONTAINS THE ALUMINUM CHLORIDE, IS THEN RECYCLED TO THE HYDROLYSIS ZONE AND THIS RECYCLE STREAM, COUPLED WITH LIQUID WASH STREAM FROM THE WASH ZONE, EFFECTS A DESIRABLE SEPARATION IN THE SUBSEQUENT SECOND SETTLING ZONE.

Jan. 12, 15971- p, w. MARSHALL ETAL 3,554,695

DISPOSAL OF SPENTRAHLUMINUM CHLORlDL ALKYLATION CATALYST, SLUGE FiledMaren 1o, 1969 lNvENToRs.

BY I

R-WxkJ/L/ m zoEjow 0 26u32 .ozoo /NN hl mzoN H mzoN @N mom n t Q mzoNIm;

JERRY MCCLESKE'Y GEORGE C. FEIGHNER DAVID W. MARSHALL mZON Ir/ wzjhbmmQNEE n 29.5..;.3 mesmo.

ATTORNEY United States Patent 3,554,695 DISPOSAL OF SPENT ALUMINUMCHLORIDE ALKYLATION CATALYST SLUDGE David W. Marshall, Severna Park,Md., Jerry McCleskey,

Franklin Lakes, NJ., and George O. Feighner, Pasadena, Tex., assignorsto Continental Oil Company, Ponca City, Okla., a corporation of DelawareFiled Mar. 10, 1969, Ser. No. 805,684 Int. Cl. C01f 7/56, 7/62 U.S. Cl.23-92 8 Claims ABSTRACT OF THE DISCLOSURE A method for separatingaluminum chloride alkylation catalyst sludge from a mixture of productalkylate and sludge, is provided wherein the alkylate is separated fromthe sludge and passed through a washing zone. The liquid employed in thewashing zone is then introduced into a hydrolysis zone wherein theseparated sludge is hydrolyzed. The hydrolyzed sludge is then allowed tosettle and form a Water phase and an organic phase. A portion of thewater phase, which contains the aluminum chloride, is then recycled tothe hydrolysis zone and this recycle stream, coupled with the liquidwash stream from the wash zone, effects a desirable separation in thesubsequent second settling zone.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to the production of alkylates.

In one aspect this invention relates to a process for the separation ofthe spent catalyst sludge obtained in the treatment of hydrocarbon withmetal halides from an Brief description of the prior art Friedel-Craftscatalysts, such as aluminum chloride, are widely used as catalysts inhydrocarbon systems, such as an olen reaction with aromatics to formalkyl aromatics, or alkyl chloride reaction with aromatics to form alkylaromatics. An important reaction which has been conducted commerciallyin the past several years has been in the manufacture of biodegradabledetergent alkylates in which aluminum chloride is employed to catalyzethe reaction of benzene with alkyl chlorides. However, in such areaction a complex of aluminum chloride and organic compounds is formedas a by-product. 'This byproduct is commonly referred to as sludge Thesludge must be separated from the detergent alkylate. While a majorityof the sludge will readily separate from the detergent alkylate uponstanding, a minor amount of the sludge remains suspended in thedetergent alkylate, along with a minor amount of dissolved gaseous HCl.The presence of the minor amount of sludge and dissolved gaseous HCl inthe detergent alkylate can have a pronounced effect upon the quality ofthe detergent alkylate. Therefore, it is desirable to remove thequantities of suspended sludge and dissolved gaseous HCl from thedetergent alkylate.

The majority of the sludge which is separated by settling or byelectrostatic induced settling has, in the past, been hydrolyzed with anexcess of water, thereby forming a dilute aqueous AlCl3 solution whichwas discarded. While it has been recognized that it would be desirable3,554,695 Patented Jan. 12, 1971 to hydrolyze the separated sludge witha smaller amount of water and recover a concentrated AlCl3 aqueoussolution which could be marketed, such has not been feasible underexisting conditions because, when one hydrolyzes the sludge with about lvolume of water per volume of sludge which is necessary to form aconcentrated A1Cl3 aqueous solution, an emulsion forms. This resultingemulsion is very diicult and impractical to break. Thus, the organicconstituents, or the AlCl3, present in the sludge cannot be separatedand recovered. Therefore, in order to recover the organic constituentsof the sludge, past practice has been to discard the dilute AlCl3aqueous phase. Thus, processes are constantly being sought wherein aconcentrated AlCl3 aqueous solution can be obtained while stillproviding separation and recovery of the organic constituents of thesludge. In addition to yielding a prot by the recovery of a concentratedAlCl3 aqueous solution and the organic constituents from spent aluminumchloride alkylation catalyst, the recovery of the aqueous AlCl3 solutionresults in the elimination of a major pollutant from plant waste waterstreams.

OBJECTS OF THE INVENTION An object of the present invention is toprovide an effective method for separating alkylation catalyst sludgefrom the alkylate.

Another object of the invention is to recover a detergent alkylatesubstantially free of dissolved HC1 gas and suspended sludge.

Another object of the invention is to provide a method for recovering anaqueous aluminum chloride solution from the spent aluminum chloridealkylation catalyst sludge.

Another object of the invention is to provide a method for recovering aconcentrated AlCl3 aqueous solution from hydrolyzed spent aluminumchloride alkylation catalyst sludge.

These and other objects, features and advantages of `the presentinvention will be apparent to those skilled in the art from the readingof the following detailed description and appended claims.

SUMMARY OF THE INVENTION According to the present invention a method forseparating spent aluminum chloride alkylation catalyst sludge fromalkylate and recovering a concentrated aluminum chloride aqueoussolution from said sludge is provided wherein the alkylation effluentcontaining the alkylate and spent alkylation catalyst sludge is passedfrom an alkylation zone into a rst settling zone so that the effluentcan form a lower sludge phase and an upper alkylate phase. The lowersludge phase is withdrawn from the lirst settling zone and passed to ahydrolysis zone where the sludge is hydrolyzed with an amount of waterelective to provide a concentrated AlCl3V solution. The hydrolyzedsludge is passed into a second settling zone so that the hydrolyzedsludge forms a water phase, containing the A1013, and an organic phase.The water phase and organic phase are separated and the water phase isdivided into a recycle stream and an aqueous product stream contaim'nglfrom about 25 to 35 weight percent aluminum chloride. The recycle streamis passed through a cooling zone and returned as a cooled recycle streamto the hydrolysis zone to maintain the temperature at the desired levelwithin the hydrolysis Zone.

The product alkylate which was originally separated from the sludge inthe first settling zone is passed through a wash zone wherebysubstantially all of the remaining gaseous HC1 and suspended sludge areremoved from the alkylate. The liquid employed as the washing medium inthe wash zone is passed to the hydrolysis zone to be mixed with therecycle stream to hydrolyze additional catalyst sludge and to cooperatewith the recycle stream to facilitate more effective settling in thesecond settllng zone.

BRIEF DESCRIPTION OF THE DRAWING The figure is a schematic flow diagramof the method of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Detergent compositions preparedfrom biodegradable alkali metal salts of linear alkyl aryl sulfonates,such as sodium salt of linear alkyl benzene sulfonates, have been widelyused in recent years. These sulfonates are manufactured by firstproducing a detergent alkylate which, upon sulfonation andneutralization, produces the biodegradable alkali metal salts of thelinear alkyl aryl sulfonates. The detergent alkylate produced by thealuminum chloride catalyzed alkylation of an aryl compound with achlorination product prepared by partially chlorinating a petroleumderived hydrocarbon fraction consisting essentially of C to C18 straightchain parafiins, as disclosed in U.S. Pat. No. 3,316,294 (1967), hasproduced a by-product known as sludge which is a complex of organiccompounds and the spent aluminum chloride catalyst.

It is to the treatment of the efiiuent from the alkylation reactionwhich contains alkylate and catalyst sludge in order to provide analkylate substantially free of suspended sludge and dissolved gaseousHCl, and at the same time, recovery of a concentrated AlCl3 aqueoussolution that the present invention is directed. The term concentratedAlCl3 aqueous solution, as used in the present disclosure is an aqueoussolution containing from about to 35 weight percent AlCl3. Theconcentrated AlCl3 aqueous solution recovered by the process of thepresent invention can be treated by any suitable method to purify saidsolution so that same can be marketed as a technical grade aqueous AlCl3solution. An effective process for purifying the aqueous AlCl3 solutionrecovered from alkylation catalyst sludge according to the presentinvention is disclosed in the co-pending application of Weiss entitled,Recovery of Aluminum Chloride From Spent Aluminum Alkylation CatalystSludge, U.S. Ser. No. 805,876 filed Mar. 10, 1969.

Referring now to FIG. 1 of the drawings there is depicted a schematicfiow diagram of the method of removing catalyst sludge from the alkylateand the recovery of a concentrated AlCl3 aqueous solution from saidcatalyst sludge of the present invention. Efiiuent, i.e. crudealkylation reaction mass, from the alkyl-ation reaction zone (not shown)is passed via conduit 11 into a first settling zone 12, wherein theeffluent is maintained at a temperature within the range of about 120 to180 F. for a sufficient period of time to allow the effluent to form alower sludge phase 14 and an upper alkylate phase 16. Preferably, theeffluent is maintained at a temperature of about 140 to 170 F. for aresidence time of about 30 to 60 minutes in first settling zone 12.After the separation of sludge phase 14 and alkylate phase 16, sludgephase 14 is withdrawn from first settling zone 12 and passed via conduit17 to hydrolysis zone 18 where sludge phase 14 is contacted with anamount of water effective to hydrolyze sludge phase 14. The water whichis fed into hydrolysis zone 18 is the wash effluent from wash zone 19,wherein alkylate phase 16 is washed to remove suspended catalyst sludgeand dissolved gaseous HC1.

Hydrolysis zone 18 is equipped with suitable agitation means so as toprovide thorough mixing of the water and sludge. The reaction mass ofthe sludge and water is maintained at a temperature of about 140 to 160F. for a period of time to allow substantially all of the sludge to behydrolyzed. When the sludge has been hydrolyzed the hydrolyzed sludge iswithdrawn from hydrolysis zone 18 and passed via conduit 21 to a secondsettling zone 22 wherein the hydrolyzed sludge forms a lower water phase23 and an upper organic phase 24. Any suitable phase separatingequipment, such as a gravity settler or electrostatic settler can beemployed as the apparatus for both the first settling zone 12 and secondsettling zone 22.

The hydrolyzed sludge is maintained in second settling zone 22 at atemperature Within the range of about 120 to 180 F. for a period of timeeffective to form water phase 23 and organic phase 24. Preferably, thehydrolyzed sludge is maintained at a temperature of to 170 F. for aresidence time of about 30 to about 60 minutes in second settling zone22. Organic phase 24 is then withdrawn from second settling zone 22 andpassed via conduit 26 to a purification and separation zone (now shown)for recovery of the desired organic constituents. Such purification andseparation processes are well known in the art.

Water phase 23 is withdrawn from second settling zone 22 via conduit 27.Water phase 23 is the concentrated aluminum chloride aqueous solutioncontaining from about 25 to 35 weight percent AlCl3. Waste phase 23passing via conduit 27 is divided into a recycle stream and a productstream. The recycle stream which is passed through conduit 28 which isin uid communication with conduit 27 is returned to hydrolysis zone 18at a rate sufficient to maintain a volume ratio of concentrated aluminumchloride aqueous solution to catalyst sludge in hydrolysis zone 18 ofabout 2:1 to 15:1. Preferably, the volume ratio of concentrated aluminumchloride aqueous solution to catalyst sludge in hydrolysis zone 18 isabout 6:1. Further, we prefer to employ a recycle stream containingabout 25 to 27 weight percent AlCl3 in order to insure that the AlCl3does not come out of the aqueous solution.

The recycle stream, prior to introduction into hydrolysis zone 18 viaconduit 28 is first passed through cooling zone 29 which is positionedbetween conduit 27 and hydrolysis zone 18. Cooling zone 29 can be of anysuitable equipment, such as a water cooled heat exchanger. The coolingof the recycle stream is important because the temperature of theexothermic hydrolysis reaction is controlled by means of controlling thetemperature of the recycle stream and passing the recycle stream intohydrolysis zone 18 so as to maintain the desired temperature rangewithin hydrolysis zone 18. By controlling the temperature and the amountof cooled recycle stream returned to hydrolysis zone 18 one can maintainthe temperature 0hydrolysis zone 18 within the range of about 120 toAlkylate phase 16 which was originally separated from lower sludge phase14 in first settling zone 12 contains a minor amount of suspendedcatalyst sludge and dissolved gaseous HCl. As previously stated, thepresence of even the minor amount of suspended catalyst sludge anddissolved gaseous HCl in the alkylate produces undesirable effects onthe quality of the product. In order to remove the suspended catalystsludge and gaseous HC1, upper alkylate phase 16 is withdrawn from firstsettling zone 12 and passed via conduit 31 to wash zone 19 wherein theundesired contaminants are removed from the alkylate product stream witha wash liquid. Preferably, the wash procedure is a continuous processwhereby the wash liquid is injected into wash zone 19 at the upperportion of wash zone 19 via conduit 32 and alkylate phase 16 isintroduced into the lower portion of wash zone 19 via conduit 31. Thewashing of the alkylate is carried out at a temperature within the rangeof about 70 to 150 F. Purified alkylate is withdrawn from the upperportion of wash zone 19 and passed via conduit 33 to a storage means(not shown). The Wash liquid, which rioW contains the suspended catalystsludge and dissolved gaseous HCl which was removed from the alkylatephase, is withdrawn from the lower portion of wash zone 19 via conduit34 and passed to hydrolysis zone 18 wherein said Wash liquid and recyclestream cooperate to hydrolyze lower sludge phase 14 and, at the sametime, facilitate the phase separation of the concentrated A1Cl3 aqueoussolution in second settling zone 22. If desirable, conduit 34 can be influid communication with conduit 28 carrying the recycle stream at apoint between cooling zone 29 and hydrolysis zone 18 as shown in thedrawing.

The wash liquid employed in the above-described countercurrentextraction of suspended catalyst sludge and dissolved gaseous HC1 fromthe alkylate is a dilute aqueous A1Cl3 or water. The wash effluent willcontain the removed A1Cl3 and thus, in effect, a dilute aqueous A1Cl3solution even when water is employed as the Wash liquid. However, caremust be exercised when employing a dilute aqueous A1Cl3 solution as theinitial wash uid to insure that the resulting concentrated A1C13 aqueoussolution formed in second settling zone 22 does not exceed 35 weightpercent AlC13 due to the decreasing solubility of the AlClg solution athigher concentrations and the HCl concentration effect on thesolubility. Desirable results have been obtained where the initial washfluid injected into the upper portion of wash zone 19 contains up toabout weight percent A1C13. It is evident to those skilled in the artthat one may need to add fresh water to either the wash effluent, therecycle stream, or the hydrolysis zone to maintain the desired A1Cl3con# contrat-ion in the concentrated aqueous A1C13 solution,

EXAMPLE I A series of experiments were conducted to determine theoptimum conditions for separation of hydrolyzed alkylation catalystsludge into an organic phase and a water phase. In each experiment thecatalyst sludge was separated from a crude detergent alkylate reactionproduct mixture obtained by the aluminum chloride catalyzed alkylationof benzene with partially chlorinated (approximately 20 percentchlorinated) C11 to C12 normal paraffins as per U.S. Pat. 3,316,294(1967). The separated sludge was then hydrolyzed at a temperatureranging from 140 to 170 F. The sludge was hydrolyzed with 1 to 2 volumesof water per volume of sludge. The hydrolyzed sludge was then passed toa settling zone which was maintained at a temperature of about 165 F.The hydrolyzed sludge was maintained in said settling zone for a periodof about l hour during which time said sludge formed a water phasecontaining A1Cl3 and an organic phase. The amount of A1C13 present inthe water phase was about 25 to 30 weight percent. The water phase wasthen divided into a recycle stream and a product stream. Varying amountsof the recycle stream were introduced into the hydrolysis zone todetermine the elfect of said recycle stream on the subsequent phaseseparation of said hydrolyzed sludge. Data illustrating the results ofthese experiments are tabulated in Table I.

TABLE I Phase Ratio (volume) separation 0 Recycle: Water: hydrolyzedsludge sludge sludge Remarks Experiment No.:

1 0:1 1:1 Poor Emulsion formed.

2 1:1 1:1 .....do Produced a thick emulsion which did not break in 5days.

3 3:1 2:1 Good Produced a fairly clear solution in about 1 hour-a clearsolution in 24 hours.

4 6:1 1:1 do i. Clear solution and good phase separation in 1 hour.

5 12:1 1:1 ,do Clear solution-good phase separation in minutes.

especially when dilute aqueous AlClg solution is employed as the washliquid.

By practicing the invention in the method contemplated the concentrationof the aluminum chloride solution generated can be maintained within therange of about 25 to weight percent A1C13 by controlling the amount ofwash liquid used to countercurrently extract the suspended aluminumchloride catalyst cludge and gaseous HC1 from alkylate phase 14 in washzone 19.

The portion of the aluminum chloride aqueous solution which is notemployed as the recycle stream is considered the product stream as tothe recovery of the aluminum chloride from the spent catalyst. Theaqueous aluminum chloride solution resulting from the treatmentdescribed in detail above contains impurities which must be removedbefore the aluminum chloride solution can be classified as a marketabletechnical grade aluminum chloride solution. The purification of thealuminum chloride solution can be by any method. However, we prefer touse that method disclosed in the copending application of Weiss entitledRecovery of Aluminum Chloride From Spent Aluminum Chloride AlkylationCatalyst Sludge, U.S. Ser. No. 805,876, filed Mar. 10, 1969.

To further illustrate the best manner contemplated for carrying out theinvention, the following working examples are set forth. As indicated,these examples are primarily given by Way of illustration, and`accordingly any emumeration of details set forth therein are not to beinterpreted as a limitation of the invention except as such limitationsare indicated in the appended claims.

The conditions employed in the above runs produced a Water phase of anaqueous aluminum chloride solution containing from about 25 to 30 weightpercent A1Cl3 (by A1 analysis) solution. A higher concentration of A1013solution can be obtained, approaching 30 to 35 percent A1Cl3, by using adilute (l5 percent) A1Cl3 solution rather than fresh water or by addingless fresh water. When employing the dilute AlCl3 solution, one stillobtains good phase separation of the hydrolyzed sludge. However, caremust be exercised to prevent the A1C13 from coming out of solution whenthe concentration of the AlCl3 is over 30 percent by Weight AlCla.However, when producing an A1C13 solution containing our preferredamount, namely 25 to 30 percent AlCl3, no problem of precipitation ofA1Cl3 is incurred. Further, the use of fresh Water is preferred ratherthan the dilute AlCl3 solution because it allows one to more easilycontrol the concentration of A1Cl3 in the solution.

In producing a concentrated A1Cl3 solution containing about 25 to 35weight percent A1Cl3, one preferably utilizes a ratio of Water to sludgeof about 1:1 in the hydrolysis zone. The data above indicates that whenusing such a ratio of Water to sludge alone an emulsion is formed.However, by employing a recycle stream containing A1Cl3 one can readilyprevent the formation of the emulsion.

EXAMPLE 1I A series of experiments were conducted to demonstrate thestep of the removal of suspended catalyst sludge and dissolved gaseousHC1 from the alkylate product stream according to the present invention.Crude alkylate reaction product mixture obtained by the aluminumchloride catalyzed alkylation of benzene with partially chlorinated(approximately 20 percent chlorinated) C12 to C14 normal parains as perU.S. Pat. No. 3,316,294 (1967) was settled to remove a major portion ofthe AlCl3 sludge present from the algylation reaction. The separatedcrude alkylate was pumped upward through a packed column containingapproximately l5 percent aqueous AlCl3 solution at a rate of 180-200mls/minute.

Two sixes of packed columns were employed in the experiments. Column No.1 was 11/2 inches in diameter and had a bed of Mz inch Raschig rings41/2 inches high with an overflow tube 11/2 inches above the bed. ColumnNo. 2 was 31/2 inches in diameter and had a bed of A1 inch Raschig rings81/2 inches high with an overflow tube approximately 3 inches above thebed. The columns were filled with a 15 percent aqueous A1Cl3 solution sothat the A1Cl3 solution covered the Raschig rings. The

eiuent crude alkylate, i.e. the washed alkylate, was collected from theoverflow and analyzed for percent AlCl3 and total acidity to determinethe effectiveness of the washing step and such results are shown in .Table II.

The above data clearly illustrates the effective removal of thesuspended sludge and gaseous HC1 from the crude alkylate by the washingstep of the present invention.

The aqueous AlCl3 solution employed in the abovedescribed washing stepcan then be used, in combination with the recycle stream, to hydolyzethe separated catalyst sludge. The ratio of the two streams, i.e. thewash effluent and the recycle stream, will be governed by the AlCl3content of the sludge being hydrolyzed and the desired concentration ofAlCl3 in the A1C13 liquor being recovered.

The foregoing discussion and description has been made in connectionwith preferred specific embodiments wherein preferred temperature rangeshave been recited in connection with the various steps employed in therecovery of a concentrated aqueous AlCl3 solution from spent aluminumchloride alkylation catalyst sludge. However, it is to be understoodthat the recited temperature ranges and the discussion and descriptionare intended to illustrate and teach those skilled in the art how topractice the invention, and such is not to unduly limit the scope of theinvention, which is to be found in the claims set forth hereinafter.

Having thus described the invention, We claim:

1. A method for recovering a concentrated AlCl3 aqueous solution fromspent A1Cl3 alkylation catalyst sludge in combination with recovering apurified alkylate which comprises:

(a) passing effluent containing alkylate and sludge from an alkylationzone into a first settling zone thereby allowing said efuent to form alower sludge phase and an upper alkylate phase;

(b) withdrawing said sludge phase and passing same to a hydrolysis zonewherein said sludge is hydrolized;

(c) withdrawing said hydrolyzed sludge and passing same into a secondsettling zone thereby allowing, said hydrolyzed sludge to form aconcentrated AlCla; aqueous phase containing from about 25 to 35 weightpercent AlCl3 and an organic phase;

(d) separating said concentrated AlCl3 aqueous phase from said organicphase;

(e) dividing said separated concentrated AlCla aqueous phase into arecycle stream and a product stream;I

(f) passing said recycle stream through a cooling zone;

(g) returning the cooled recycle stream to said hydrolysis zone at arate effective to maintain a volume ratio' of recycle stream to sludgein said hydrolysis zone: of about 2:1 to 15:1 and at a temperatureeffective to maintain the temperature in said hydrolysis zone within therange of about 140 to 160 F;

(h) passing the alkylate of step (a) through a wash zone containing awash liquid to remove substantially all of the remaining gaseous HC1 andsus` pended AlCl3 sludge from said alkylate and recovering from saidwash zone a purified alkylate; and

(i) passing said wash liquid to said hydrolysis zone to cooperate withsaid recycle stream to hydrolyze said sludge and facilitate phaseseparation of said hydrolyzed sludge in said second settling zone.

2. The method of claim 1 where said effluent in said first settling zoneand said hydrolyzed sludge in said second settling zone are maintainedat a temperature within the range of about to 180 F.

3. The method of claim 2 wherein said efliuent and said hydrolyzedsludge are maintained at a temperature within the range of about to 170F. for a residence time of about 30 to 60 minutes.

4. The method of claim 3 wherein said wash liquid is selected from thegroup consisting of water and dilute aqueous AlCl3 solution containingup to about 20 weight percent AlCl3 and the washing step is carried outat a temperature Within the range of about 70 to 150 F.

5. The method of claim 4 wherein said concentrated AlCla aqueous recyclestream contains about 25 to 27 weight percent AlCl3.

6. The method of claim 5 wherein said alkylate is passedcountercurrently through said wash zone and said method of recoveringsaid concentrated A1Cl3 aqueous solution is a continuous process.

7. The method of claim 6 wherein said cooled recycle stream is returnedto said hydrolysis zone at a rate effective to maintain a volume ratioof recycle stream to sludge of about 6:1.

8. The method of claim 7 wherein said sludge is hydrolyzed with about a1:1 volume ratio of water to sludge.

References Cited UNITED STATES PATENTS 2,228,707 1/1941 Roberts et al.23-96X 2,471,054 5/1949 Amick, Ir. 23-96X 2,525,830 10/1950 Sailors etal. 2396 3,316,294 4/1967 Feighner et al. 260-505 EDWARD STERN, PrimaryExaminer U.S. Cl. X.R. 260-505, 683.53

